Manufacture of sodium carbonate from salt residues left by the evaporation of alkaline waters



P" 1932- A. c. HOUGHTON ETAL 1,353,275

MANUFACTURE OF SODIUM CARBONATE FROM SALT RESIDUES LEFT BY THEEVAPORATION OF ALKALINE WATERS Filed Dec. 28, 1929 M4 00; NA 60 r/VA6LH0 flutes G). ZYZZZer n zrmw i- Patented Apr. 12, 1932 UNITED STATESPATENT OFFICE ALEXIS C. HOUGHTON, OF BARTLETT, AND JAMES G. MILLER, 01LONE PINE, CALIFORNIA MANIIFAGTURE F SODIUM CARBONATE FROM SALT RESIDUESLEFT BY THE EVAPO- RATION OF ALKALINE WATERS Application filed December28, 1929. Serial No. 517,136.

In our prior Patent No. 1,759,361 issued to us on May 20, 1930, we havealready disclosed a method for the separation and recovery of sodiumcarbonate in a purified state from complexnatural brines containing thesame by chilling such brines after making them sufiiciently alkalinewith a caustic alkali to prevent precipitation of silica, such inventionrelating more particularly to the production of a sodium carbonate inthe form of decahydrate crystals suitable for the manufacture of causticsoda.

Our present invention relates more particularly to the manufacture ofsoda ash from the waters and deposits of Owens Lake, California,although we do not Wish to limit our invention to the deposits of thisparticular lake, as the process is applicable to either natural orartificial brines, deposits, or mixtures of solid salts of the generalnature and composition of those found in Owens Lake, and consistingprincipally of the chlorides, carbonates, sulphates, and borates ofsodium and potassium.

The method used commercially up to the present time for the manufactureof soda ash from the brines or deposits of Owens Lake is that ofcarbonation, which consists in passing into the brine carbon dioxide gaswhich reacts chemically with the sodium carbonate contained therein toform sodium bicarbonate or sodium sesquicarbonate, which substancesbeing less soluble than sodium carbonate crystallize out and may beseparated by filtration, and after washing free from mother liquor becalcined to produce sodium carbonate commercially known as soda ash.This method has obvious disadvantages, the principal of which are thenecessity of the quarrying and transportation of limestone, purchase andtransportation of coke for burning the limestone, installation 'of limekilns, carbonating towers, compressors for forcing the gas through thebrine, and the calcining of the resulting sodium bicarbonate orsesquicarbonate in furnaces at the relatively high temperature of 200 to300 C. to effect its chemical decomposition to sodium carbonate,necessitating considerable expense for fuel, all'of which is avoided inour process, thereby greatly decreasing the investment and operatingcosts. Also the calcium and magnesium oxide which results from drivingofi the carbon dioxide from limestone or dolomite is a waste product anda direct economic loss, such calcined lime being generally piled up inwaste piles or puddled away to the lake. Further, the soda produced bythe carbonation method is a more or less impure product, beingcontaminated by silica, sodium borate, and org)anic matter im urities.The brines of wens Lake contain considerable amounts of dissolved silicaand organic matter, such silica being held in solution by the degree ofalkalinity of the original brine. When the brine is rendered lessalkaline by the introduction of the acid carbon dioxide, a largeproportion of this dissolved silica is precipitated in a gelatinous orcolloidal form, which also carries down organic coloring matter,rendering the precipitated sodium bicarbonate difficult to wash freefrom mother liquor, and also contaminating the product with silica andorganic coloring matter carried down with the colloidal silica. Alsothis brine contains sodium borate principally in the form of themetaborate, which is very soluble. On carbonation this is partiallyconverted into the more insoluble tetraborate, which is precipitated tosome extent with the sodium bicarbonate and cannot be entirely freedtherefrom by washing, but goes over into the final product tocontaminate same.

It is the principal object of our invention to avoid the undesirable anduneconomic features of the carbonation process, and to provide a simplerand more economical method of manufacturing soda ash from these brines,involving only the principles of crystallization, and at the same timeto make a purer product practically free from silica, organic matter, orborate impurities.

' The principle of our invention is the preparation of a suitable andstandard brine,

not subject to seasonal changes of composition, and of such compositionthat when chilled to such a temperature as will permit a recovery ofover fifty percent of its contc ir ed sodium carbonate. the onlyconstituent cryshydrate, which may be removed by filtration or othersuitable means and washed free from adhering mother liquor. Thedecahydrate crystals may then be dried directly to soda ash in asuitable furnace, or preferably they may be melted in their own water ofcrystallization and the resulting solution evaporated, whereby sodiumcarbonate monohydrate crystallizes out, which is removed, washed freefrom mother liquor, and dried at a temperature around 100 C. to giveanhydrous sodium carbonate. It will be seen that in our process thesodium carbonate receives two crystallizations and washings, whichresults in a final product of much greater purity than that manufacturedby the carbonation process, or even than the soda ash manufactured bythe ammonia soda process.

As our process deals mainly with the phenomena of crystallization andequilibrium conditions of saturated solutions containing several salts,it will be necessary for the more ready explanation and understanding ofour invention to refer to certain applications of the phase rule as theconcern the influence of one salt on the solubility of another, whichapplications are of fundamental importance in the study of this crystalbody and the resulting brines. The principal salts found in thecrystallized state in the crystal body of Owens Lake are sodiumcarbonate decahydrate, sodium carbonate monohydrate, sodium chloride,and a double salt of the composition Na CO .2Na SO Although otassiumchloride is always a constituent '0 these brines, it is not necessary toconsider it here for the reason that the brines under natural conditionsnever reach saturation in this salt, and it is not therefore animportant factor in the equilibrium reactions. We shall therefore limitour equilibrium diagrams to the four component system sodium carbonate,sodium sulphate, sodium chloride, and water. Careful studies of thisfour component system are available in the chemical literature and thediagrams we give are from the published diagrams of this system at thetemperatures respectively of 20, 35, 50, and C. Diagram A represents thesolubility relations existing between these salts or their hydrates atthe temperature of 20 C. represented according to the well known methodof Schreinmakers, which will be readily understood by those skilled inthe art. That is, it is a projection on a horizontal plane of a spacefigure constructed on the faces and in the interior of a regulartetrahedron, the three corners of the base of each tetrahedron eachrepresenting 100% of the pure salt, and the vertex or fourth cornerrepresenting pure water. The saturation curve for any two of the saltsin water, and mixtures thereof. are drawn on each of the three faces ofthe tetrahedron which have the water corner in common, and where twosuch saturation curves meet in a point on one of the three faces, thispoint represents an invariant solution saturated with the two salts atthe temperature for which the diagram is made and at atmosphericpressure. The saturation curves of the various mixtures of three saltsand water are drawn from these invariant points on the faces towards theinterior of the tetrahedron. The plane figures shown are projections ofthis space figure in a horizontal plane on the base of the tetrahedron,the projection of the various lines and points being by means ofparallel lines perpendicular to the base. The vertex of the tetrahedron,which represents pure water, projects into the point W, or the centroidof the equilat-' eral triangle representing the base. The saturationsurfaces of the three single salts or their hydrates, and of the doublesalt N a"- CO .2Na SO are clearly shown, and lines Na CO .NaHCO .2H O,

around the shallower margins of the lake. This trona is more or lessimpure, containing entrained sodium chloride, sulphate and borate, andalso in portions of the lake it is overlain with a layer of siliceousmud. On account of these facts, and the fact of its limited solubility,the trona deposits do not readily lend themselves to form the basis ofan economical process for the manufacture of soda ash. Also the marginaldeposit-s of trona are gradually being washed down to the central basinof the lake by rains and surface waters entering the lake by means ofvarious creeks and springs, and will in the course of time no doubt beentirely washed down to the central basin. The main alkali content ofthe lake is contained in the deeper central basin, which is composed ofa more or less solid body of crystallized salts from four to seven feetin thickness, but permeated in the interstices of the crystal mass witha saturated brine much after the fashion of a sponge. We have devisedour process for this main cilystal body as being more permanent in sup-P .V-

It is known that there are two distinct types of brine in the maincrystal body. At about 24 to 30 inches below the surface of the lakethere is a hard layer or series of layers of sodium chloride. The brinesabove this layer are known as surface brines, while those below aredesignated sub-surface brines. There is comparatively very little mixingbetween the two types of brines.

The surface brines are subject to wide sea-' sonal fluctuations oftemperature and composition, the temperature varying from about 6 C. inthe winter to from 50 to 60 C. in the hot summer months. The sub-surfacebrines are more uniform in temperature the year around, with a minimumtem erature of about 12 C., and a maximum of a out 22 C. Following areanalyses of sub-surface brines representing minimum, average, andmaximum temperature conditions, such brines being designatedrespectively \Vinter, Average, and Summer.

Winter Average Summer NazCOa equivalent 9. 18 12. 72 15. 87 NSICOIactual 12. 40 NaHCOg. Not det'd 50 Not detd NBQBQOA l. 2. 26 2. 50 2. 37Nags 5. 38 4. 71 3. 79 NaCl ll. 20 KC] Not detd 3.00 Not detd NaClequivalent. 16. 13. 56 i1. 70 a i0; Not detd .30 Not dct'd Na HP04 Notdet'd .33 Not detd Organic matter, other salts,

and water 65. 06

Total 100. 00

By NagCO equivalent we mean the total alkali of the Na CQ, and NaHCOexpressed as Na CO By NaCl equivalent we mean the total chlorine of theNaCl and KCl expressed as NaCl.

In our aforementioned prior patent we have described our process ofchilling these brines to obtain sodium carbonate in a purified statesuitable-for the manufacture of caustic soda. When a brine of theaverage composition already given containing 12.72% Na CO equivalent and4.71% Na SO is chilled to a suitable temperature, there is noprecipitation of sodium chloride or sodium borate, and it is possible toprecipitate 50 to of the total sodium carbonate content of the brine asessentially pure sodium carbonate d'ecahydrate. There is however alwaysmore or less sodium sulphate decahydrate precipitated also, which is notreadily removable with the mother liquor by washing the crystals. Onaccount of the strong tendency of sodium sulphate to form supersaturatedsolutions, if the refrigeration is performed in a reasonable time, saytwo hours, the sulphate content in the crystals may be kept down to aproportion of from 3 to 10 parts of Na- SO, to 100 parts of Na CO Withthe winter type brines however with low sodium carbonate and high sodiumsulphate content, it is impossible to avoid considerable precipitationof sodium sulphate when the brine is cooled to such a temperature aswill give over 40% recovery of the total sodium carbonate present. Theresulting decahydrate crystals from the winter brine may contain aproportion of sodium sulphate as high as from 20 to 30 parts of Na SO to100 parts of Na CO Such a pro portion of sulphates, while not desirable,would not be prohibitive for the manufacture of caustic soda for thereason that when the sodium carbonate solution is causticized and theresulting NaOH solution evaporated to 48% NaOH, practically all of thesodium sulphate separates out and can be removed, be-

'ing quite insoluble in the strong caustic liqour. Too high a proportionof sulphate, however. would be absolutely fatal for the manufacture ofsoda ash of high purity from the clecahydrate crystals. Reference to thediagrams, and the calculations we shall give which may be made from thecomposition of the solutions that the diiferent points represent, willmake this point quite clear. By the term solution used in the followingdiscussion is meant the clear mother liquor in contact with the crystalsor solid phase at the particular temperature.

In diagram C for instance, on the H 0- l la CO --l Ta SO. face of thetetrahedron, point 4 epresents a solution saturated with respect to thesingle salt of Na CO I-LO at 50 C. As the curve approaches point 5 thereare increasing amounts of sodium sulphate in solution, but another solidphase beyond the NfigCOgH-zO already present does not appear until point5v is reached. At this point the solution just becomes saturated withthe double salt Na CO .2Na SO,, which will then commence to crystallizeout, so that point 5 represents a solution in equilibrium with both thesolid phases Na cO l-LO and the double salt Na CO .2Na SO If then weevaporate at 50 C. an unsaturated solution of sodium carbonatecontaining a small amount of Na S0 at first only sodium carbonatemonohydrate will crystallize out, the solution increasing in sulphatecontent until it reaches a concentration represented by point 5, when onfurther evaporation both monohydrate and the double salt will crstallizeout in the exact proportion in which they exist in the solutionrepresented by point 5, and the solution will remain of constantcomposition until the water is completely evaporated, point 5 being whatis known as the drying-up point. If the object, therefore, is to makepure sod um earbonate monohydrate from a solution containing sodiumcarbonate and a small amount of Na SO,, the solution can only beevaporated up to or just short of a composition represented by point 5in order to ensure that the only solid phase separating out is sodiumcarbonate monohydrate. The amount of sodium sulphate originally presentin the sodi- I Composition of solution Ratio in the solution of K sPoint g NazCOa NazSO4 NazC03 Nag If we take 50 C. as a practicaltemperature atwhich to evaporate the melted decahydrate crystals under agood vacuum, it will be seen that if the ratio of sulphate to carbonateis 14.3 or more of Na SO to 100 of Na CO there can be no separation ofpure sodium carbonate monohydra-te, as the moment sodium carbonatemonohydrate commences to separate out, there will be a simultaneousseparation also of the double salt. The ratio of sulphate to carbonatemust be lower than this figure, and the lower the sulphate the higherwill be the percentage recovery of the total sodium carbonate content ofthe solution as pure monohy'drate. This will be apparent from thefollowing table giving approximately the theoretical recovery of thetotal sodium carbonate present as pure sodium carbonate -monohydrate byevaporating solutions containing sodium carbonateand sodium sulphate inthe following proportions It will be seen that in the manufacture ofsoda ash of high purity it is of fundamental importance to keep theamount of sodium sulphate in the refrigerated decahydrate crystals downto a minimum figure.

The foregoing is merely to illustrate the principles underlying ourinvention using the two pure salts sodium carbonate and sodium sulphate.It is to be understood that in practice there will be small amounts ofsodium chloride and sodium borate also in the solution obtained bymelting the decahydrate crystals due to incomplete washing out of themother liquor, but the presence of small amounts of these salts will notmaterially af feet the fi ures given above.

While y refrigeration of sub-surface brines of the winter type it wouldbe possible to make a soda ash of high sodium sulphate content whichwould be acceptable for the purpose of glass making, where to someextent sodium carbonate and sodium sulphate are interchangeable, suchsoda ash would not be acceptable to the general and export traderequiring high purity. If it were proposed to use only the average andsummer type brines, so that the sulphates could be kept down to aworkable figure to make high purity soda ash at a reasonable yield,there is the economic objection that this could be done only from sevento eight months of the year, as the winter type brine persists for aboutfour or five months. It is the principal object of our invention toprovide a process which will make high purity soda ash from these brinesand deposits every day in the year, independent of seasonal fluctuationsin temperature and composition, and we achieve this end-by modifying thebrines in such a manner as to reduce their sodium sulphate content to aworkable figure by a very simple and inexpensive process which takesadvantage of certain equilibrium relations, which will be fullyexplained later.

To illustrate the degree to which the sul phate content must be reducedin the brine, we give below a table showing the composition of thesolution in equilibrium with the crystals of sodiumcarbonatedecahydrate, sodium sulphate decahydrate, and sodium chloride at thetemperatures 12, 10, and 6 C. It is necessary to consider thisequilibrium in the presence of the solid phase sodium chloride, for thereason that when sodium carbonate decahydrate is crystallized out of thebrine, there is an increase in concentration of the sodium chloride andother constituents due to the abstraction of water from the solution aswater of crystallization with the sodium carbonate decahydrate. While itis true that the solubility of sodium chloride in the mother liquorincreases, as the percentage of sodium carbonate is reduced, if thecooling is carried far enough so that there is sufficient abstraction ofwater with the decahydrate, a point will be reached at which the motherliquor becomes saturated with sodium chloride, and if the cooling iscarried below this point sodium chloride will crystallize out. If thesulphate is sufficiently low, therefore, this precipitating point ofsodium chloride will limit the degree to which the brine may be cooledto obtain only sodium carbonate decahydrate. The equilibrium pointsgiven are in solutions containing the same concentrations of sodiummetaborate and potassium chloride as are found in the lake brines.Unless extreme chilling is employed, say down to zero degrees centigradeComposition of solution in equilibrium with solid phase NazCOa. 101120,Na:SO4.lOHa0, and NaCl 12C. 10 C. 6 C.

% Naiooim 7. 37 6.32 4. 61 N8QSO4 5. 55 4. 26 2. 73 NBC] 17. 69 19. 0121. 28

From these figures the following table is calculated showing the maximumsodium sulphate content permissible in brines of different strengths insodium carbonate, so that when such brine is cooled down and equilibriumattained at the indicated temperature, no sodium sulphate willcrystallize out, and also showing the percentage recoveries of the totalNa CO present at the different temperatures to which the cooling iscarried.

Maximum Na SO; permissible in brines if cooled to- Nmooi in brines Percent recovery of total NmCOi as decahydrate when cooledto- 12C. 10 C. 6C.

While decahydrate crystals with a fairly low sulphate might be obtainedfrom brines containing sulphate over the above limits due to the wellknown tendency of sodium sulphate to form supersaturated solutions andtherefore not precipitating out or coming to equilibrium in the periodof cooling, yet the phenomena of super-saturation and metastable statesare so tricky and uncertain that it would not be practical to base acommercial process on the chance of always obtaining supersaturatedsolutions except in a few very exceptional cases where the metastablestate is very persistent. i The above figures still further emphasizethe difiiculty of hi h sul hate with the winter brine, as in orfer to 0tain a workable yield of Na cO say over 50%, it would drate,

be NaCl equivalent, and

necessary to cool thebrine to 6 C. or thereabouts, and a sulphatecontent of more than 2.35% could not be safely tolerated, whereas theactual sulphate content of winter brines composition of the solution atthese points at the difi'erent temperatures is as follows Temp. o. PointNa,cc= %Na|SO4 %NaCl 20 1 14. 2 4. 1 15. 4 35 3 16. 1 l. 8 15. 4 50 61a. 5 1. a 17.8 75 8 l1. 2' 1. 0 20. 4

It will be seen that if high sulphate brine is stirred or agitated .withexcess of the solid phases sodium chloride, and either sodium carbonatedecahydrate or monohydrate, whenequilibrium is attained the compositionof the brine will approximate to that given above at the temperatureemployed. The sodium sulphate will be taken out of solution from thebrine by combining with sodium carbonate to form the double salt Na CO-.2Na SO,, which will crystallize out down to its solubility representedby the points given above, and as long as excess of the three solidphases sodium carbonate hysodium chloride, and the double salt arepresent, the sodium sulphate in solution in the brine must be reduced tothe fi ures given above. For instance if a winter rine containing 9.18%M 00. and 5.38% Na SO is agitated at 35 C. with an excess of sodiumcarbonate monohydrate and sodium chloride, or even with sodium carbonatemonohydrate alone, as there is'already suflicient sodium chloride in thebrine to be oversaturated with this constituent when equilibrium isreached at 35 (1., then the double salt Na CO QNa SO will be formed andcrystallize out, the solution will saturate up to around 16.0% Na CO andthe brine when settled clear will only contain 1.8%Na SO There arevarious ways of bringing about the desired condition of having an'excessof the solid phases sodium carbonate hydrate, sodium chloride, and thedouble salt NagCO -2Na2SO4 in contact with the brine at a temperaturehigh enough to give a sulphate content below the limit sought, a few ofwhich will be mentioned. We may, for instance, take a brine 0f thecomposition 9.18% Na CO 5.38% 'Na.,SO and 16.19% by solar evaporation orother means evaporate it to a point where an excess of sodium carbonatemonohydrate and sodium chloride has crystallized out. Under theseconditions, if the temperature is higher than the point at which thedouble salt becomes stable in contact with the solution, the double saltNa CO 2Na SO will be formed and crystallize out, and the resulting brinewill be lowered in sulphate content, the degree of such loweringdepending on the temperature at which the brine is evaporated. Or wemay, for instance, take a clear summer brine of the composition 15.87%Na CO 3.97% Na sO and 11.70% NaCl equivalent, add excess of solid sodiumchloride, the brine being undersaturated with this constituent, and heatit up to 50 C. with agitation. Under these conditions it will becomesupersaturated with Na CO .H O and the double salt Na CO 2Na SO and whenequilibrium is reached these salts will crystallize out, and theresulting brine, although it may not have reached the equilibriumcondition at 50 represented by point 6 on account of the insufficiencyof Na CO to combine with the excess of sodium sulphate present, and sowill contain more than the 1.3% M 50 represented by that point, stillthe sulphate content will be lowered to the permissible figure or lower,so that when the brine is chilled-to a suitable point to give over 50%recovery of its contained sodium carbonate, no sodium sul hatedecahydrate will crystallize out.

ur preferred method of operation, how- Y ever, is not to use thesubsurface brines. \Ve

prefer to operate on the surface of the crystal body, thereby takingadvantage of solar evaporation to bring about the conditions describedin the foregoing. In the arid and windy climate of the Owens Lakeregion, especially in the summer, conditions are very favorable forevaporation, and the brine at the surface of the lake on the crystalbody is continuously depositing sodium chloride, and either sodiumcarbonate decahydrate or monohydrate, depending on the temperature,

perature decreases the saturation surface of the double salt graduallygrows smaller, and at some temperature below 20 C., possibly around 18C. where the saturation surface of anhydrous sodium sulphate disappears,the saturation surface of the double salt also disappears. In otherwords at some temperature below 20 C. the double salt N a CO 2Na SObecomes unstable in contact with the solution, and decomposes into itsconstituents sodium carbonate and sodium sulphate. \Vhat happens on thesurface of the lake, therefore, is that in the summer, when thetemperature is high, the double salt Na CO 2Na SO is formed andcrystallizes out in the solid phase in contact with the saturated brine.When the brine cools off in the winter a temperature is reached at whichthe double salt can no longer exist in contact with the brine, and thecrystals of this double salt are therefore decomposed, the brinebecominghigh in sodium sulphate. The composition of the clear surfacebrine in winter and summer given below clearly illustrates this point.

The cOmp-o i [ion of the solid phase or crystalline salts in contactwith the saturated brine in the hot summer months, after separating samefrom the mother liquor, is approximately as follows:

% NaCl equivalent 83.29 Na CO lLO 6.90 Na CO 2Na SO 8.50

NEIQB3O. Y .63

K, Calc. as K2804 .80

The small amount of potassium present shows that the formation ofglaserite, Na SO .3K O is not an appreciable factor in lowering thesulphate content of the summer brine, and that we have to deal only orprincipally with the double salt Na CO 2Na SO as the chief factor in thereactions which take place which are responsible for reducing thesulphate in solution. As the brine has the maximum amount of sodiumcarbonate in solution in the summer, and as in the winter the sodiumcarbonate content of the solid phase or crystal body must be stillfurther increased by the deposition or chilling out of sodium carbonatedecahydrate crystals from the high Na CO content summer brine, itfollows from the above analysis of the solid salts that there mustalways be an excess of either sodium carbonate monohydrate ordecahydrate as a solid phase'in thecrystal body at the surface at anytime during the year, and also always an excess of NaCl. \Ve takeadvantage of this fact in our preferred method of operation. In thesummer months of July, August, September, and part of October, the clearsurface brine with its content of sodium sulphate below 2%, is ideallysuited for the application of our refrigeration process, the only saltseparating out on cooling to say 10 C. eing sodium carbonatedecahydrate. If the cooling is carried further than this there might besome precipitation of sodium chloride, but if the higher recovery ofsodium carbonate in going to a lower temperature more than pays for theincreased cost of refrigeration, this difliculty is easily remedied byadding water to the brine to allow for the water abstracted with thedecahydrate to prevent the mother liquor from becoming saturated withsodium chloride. In the summer months mentioned it is therefore onlynecessary to pump the clear surface brine to the plant, make itsutficientl alkaline with a caustic alkali to prevent t e precipitationof silica and organic matter as disclosed in our previously mentionedprior patent, and apply the refrigeration process.

For the remaining eight to nine months of the year, one method ofprocedure might be to build a storage pond or reservoir large enough tohold-an eight to nine months supply of brine, and fill it with the clearsummer surface brine of the desired composition. Such brine could bewithdrawn to the plant as needed, or if the pond were provided with anoutlet at its lowest point capable of being closed or opened, the wholebody of brine could be allowed to cool under the winter temperaturesprevailing, and separate out sodium carbonate decahydrate, and themother liquor drained ofi from the bottom outlet. The crude decahydratecrystals remaining in the reservoir, with their adhering or entrainedmother, hquor, and then be mushed up and their contained mother liquorseparated by centrifuging and'the crystals washed, or the crudedecahydrate crystals could be melted up by steam or water, and theresulting more or less purified'sodium carbonate solution subjected topurification by refrigeration or other means in the plant. We have,however, sought to avoid the building, maintaining, and operating oflarge storage or evaporation ponds as not being entirely practical oreconomical, and adding needlessly to the investment and operatingexpense. Our preferred method of operation in the months when lowtemperatures and high sulphate brines persist, which may be taken asfrom the middle of October to the middle of June, is to mix up bystirring or hydraulicking with brine, or any suitable mechanical orother means, the mass of crystals and brine naturally existing on thesurface of the lake, and to pump such mixture into a tank'provided withan agitator and a pipe for admitting steam, The'thin mush of brine andcrystals composedprincipally of sodium carbonate decahydrate and sodiumchloride, is agitated'in the tank and steam admitted directly into themass until the temperature reaches the desired point, when the stirringis scribe and in t continued long enough for the double salt ITa CO .2lTa SO to crystallize out and to approach equilibrium with the threesolid phases sodium carbonate monohydrate, the double salt, and sodiumchloride, the temperature being maintained at the desired point in themeantime by admitting steam when necessary. The agitator or stirring isthen stopped, and the brine allowed to settle out the excess of salts,the clear brine being decanted otl' and pumped to the plant forrefrigeration. Direct steam may be admitted for the heating for thereason'that there will be a more economical utilization of its heat byadmitting it in this manner rather than transferring its heat throughthe medium of heating coils. The dilution thus caused by thecondensation of water from the steam will not affect the equilibrium aslong as it is not excessive, because there is always present an excessof the solid phases and the brine will therefore always reach saturationat the temperature employed. The salts which settle out and from whichthe clear brine has been decanted, may be used for another batch ofbrine as long as the free sodium carbonate content of the salts has notbeen exhausted, or they may be returned to the lake if exhausted in thisconstituent. It is desirable to secure a brine, which while lowenough insodium sulphate so that sulphate will not crystallize out in thesubsequent cooling, will have a maximum sodium carbonate and a minimumsodium chloride content, so that a long cooling range may be used and ahigh recovery of sodium carbonate obtained without the danger of sodiumchloride crystallizing out. We have found that there is an optimumtemperature to which the brine may be heated where the sodium carbonatecontent is at a maximum and the sodium chloride at a minimum, thistemperature being in the neighborhood of 30 C. By careful regulation ofthe temperature to this point in saturating the brine in the presence ofthe excess of the solid phases, we have found it possible to produce abrine containing 16.75% Na COa and 13.00% NaCl, with sulphates below thedesired figure. For practical operation, however, we have found that abrine containing 16% Na cO- and 14% NaCl, with a sul hate content of2.8% N a SO may be readi y obtained after two hours stirring of themixture at a temperature varying between 28 and 32 C. If it were desired.and it was an economic advantage to do so, a brine of this compositioncould be secured every day of the year b heatin in the winter season asdelue summer by cooling the agitated mixture of brine and salts withcooling coils to a temperature of 30 (3., and it is one of the greatadvantages of our invention that it is possible if desired to absolutelystandardize the process by securing in this manner a. brine of standardand invariant composition the year around by the simple expedient ofmaintaining a constant temperature at which the brine and salts areagitated together, thus rendering our process entirely independent ofseasonal changes and fluctuations in natural temperature or composition,such seasonal fluctuations hitherto being one of the great handicaps ofthe soda ash industry on Owens Lake. Such a standard brine of theaforesaid composition when cooled to 10 C. will ive a recovery of about73% of the total Na 0 present in the form of sodium carbonatedecahydrate crystals, with no precipitation of chlorides or sulphates.We hay e found that a loss of about 7% Na C0 is sustained by washing thedecahydrate crystals on the centrifuge free from mother liquor to thedesired degree, lowering the recovery of the total Na CO originallypresent in the brine to about 66%. As the recovery of pure monohydratecrystals on evaporating the melted decahydrate crystals should be 90% ofthe sodium carbonate present, and 85% after washing on the centrifuge,the over-all recovery of the sodium carbonate in the original brine ashigh purity soda ash is well over 50%.

If it is desired, we may of course use our process for the commercialmanufacture of sodium carbonate monohydrate of high purity by simplyomitting the final step of converting the monohydrate into anhydroussodium carbonate, in which case after washing the sodium carbonatemonohydrate crystals on the centrifuge, they would be suitable formarketing as such, or if it were desired to remove the mechanicalmoisture without driving off the water of crystallization, they could beair dried, or dried in a drier at a temperature low enough (below 80 C.)so that the molecule of water of crystallization would not be removed.

Having now fully explained the principles underlying our invention, wewill give a specific example of how it may be carried out in practice.Located directly on the crystal body of the lake we employ a tank ofsuitable size and supplied with an agitating device and means ofadmitting steam, and also with coils for cooling if necessary. Adjacentto this tank on the crystal body we make a mixture on the surface of thelake, in a pool, of the surface brine and salts as they naturally exist,by any suitable mechanical or other means, and pump this mixture ofbrine and salts into the aforementioned tank. The mush of brine andcrystals is then agitated, and either heated by the direct admission ofsteam, or cooled by means of the cooling coils and cooling water.depending of course on the natural temperature of the brine. until anapproximate temperature of 30 C. is attained by the mass. The agitationis continued and the temperature maintained at this point for about twohours, by which time, although complete equilibrium as regards theformation of the double salt or sulphate content of the brine may nothave been reached, the sodium sulphate content Will be reduced to thelimit desired. The agitation is then stopped and the excess of saltsallowed to settle out of the brine, and when the brine is sufficientlyclear it is decanted off and pumped to the plant. The composition of thebrine at this point will be In the plant to 10,000 pounds of this brineis added 20 pounds of actual NaOH in the form of a 48% solution of NaOH.This converts the NaHCO present to 'Na CO and leaves a slight excess ofabout 0.2% NaOH in the brine, which we find is suflicient to hold allthe silica in solution during the subsequent cooling operation. Or wemay employ the cheaper calcium hydroxide as the caustic alkali for thispurpose, in which case we add the requisite amount of milk of lime ofabout 200 grams per liter active CaO content. If lime is used it will benecessary to settle out or separate from the brine the small amount ofinsoluble calcium carbonate formed in the reaction. The brine thustreated is then cooled down to 10 C. in a suitable vessel orcrystallizing tank. \Ve may performthis cooling by artificialrefrigeration by means of any form-ofv ice machine and cooling coils orjackets, or we may cool the brine by allowing it to evaporate in asuitable closed tank under a very high vacuum, the cooling in this casebeing performed by the evaporation of a certain amount of water (whichwould be previously added to the brine), and the maintenance of a'veryhigh vacuum to reduce the boiling point of the solution to 10 0., or wemay use a combination, in steps, of vacuum cooling and mechanicalrefrigeration. We prefer to allow a period of at least one hour and notmore than two hours in which to bring the temperature down to 10 C. inorder to build up the size of the decahydrate crystal such as may bereadily filtered and washed. When the temperature has reached 10 C. themush of sodium carbonate decahydrate crystals and mother liquon isdischarged to a centrifuge, or the crystals filtered by other suitablemeans, and then washed as free as possible from themother liquor bymeans of cold water. The mother liquor may be returned to the lake, ormay be reserved for the recovery. of other products, as potassiumchloride or borax. I If the method employed is that of centrifuging,there will be obtained These crystals will be snow white and will givewith water a clear water white solution practically free from organiccoloring matter. If it is only desired to make a low grade ash ofabout95% Na CO content, the crystals may be dried directly to soda ash in anysuitable furnace or drier. Or if it is desired a very eflicient washingmay be given the decahydrate crystals on the centrifuge to removepractically all of the mother liquor impurities, in which case thewashed decahydrate crystals may be dried directly to soda ash of highpurity. Our preferred method however is to take advantage of the furtherpurification effected by the crystallizing out of sodium carbonatemonohydrate when the water content of the decahydrate crystals ispartially evaporated ofl in an evaporator. To this end we melt up thedecahydrate crystals by the application of heat, and obtain 3110 poundsof solution of the approximate composition Na CO 34.0 so Na2SO, .4 Na BO -2 NaCl .4 SiO .007 H O 65.0

Total 100.00

This solution is fed to a vacuum evaporator of suitable type, and 1557pounds of the 2021 pounds of water present evaporated oil. The resultingmush ofsodium carbonate monohydrate crystals and mother liquor iscentrifuged or filtered, and the crystals washed on the centrifuge orfilter with cold water to free them from'mother liquor as completely aspossible. There will be obtained approximately 1117 pounds ofmonohydrate crystals contalning about 6% mechanical moisture. Thesecrystals are dried in a drier at approximately 100 C., such drier beingoperated by waste heat, by air heated over steam coilsprovided withexhaust steam, or other method, such economical method of dr ing beingmade possible by the fact that so ium carbonate monohydrate loses itsmolecule of water of crystallization at atemperatu're below 100 C., anddoes not melt in its water of crystallization as does the decahydrate.

There will be obtained from this drier about 903 pounds of soda ash withabout the following analysis Na CO 99. 46 Na B O. .07 Na SQ, .19 NaCl.23 SiO .04

Total 99. 98 Total Na O 58. 16

This represents a recovery of the total Na CO present in the original10,000 pounds of brine of 56% as high purity soda ash. Such soda ashwhen dissolved in pure water will give a perfectly clear Water whitesolution, free from suspended silica or organic coloring matter, whichis not the case with any soda ash at present made on Owens Lake bythecarbonation method.

Orif it were desired to make sodium carbonatc monohydrate of high purityas a commercial product, the 1117 pounds of monohydrate crystalscontaining about 6% of mechanical moisture could be marketed in thatstate, or the crystals could be freed from mechanical moisture in asuitable drier in which the temperature was kept below that at which themolecule of water of crystallization would be driven oil.

Our invention may also be applied to a mixture of dry salts containingsodium carbonate, sodium sulphate and sodium chloride.

4 If for instance the deposit in Owens Lake or other similar basinscontaining the same salts, should dry up completely, the salts wouldstill be there in the same proportions as at present, and all that itwould be necessary to do according to the principles of our invention,would be toadd a limited amountof water and stir the water with thesalts at a temperature of around 30 C. until the water became saturatedwith the salts. If not too much water was added we should arrive at thesame equilibrium point as previously described, and obtain a brine ofthe standard composition previously iven, to which our refrigerationprocess cou d be applied.

Or for instance the mother liquor obtained fromcooling the brine andfiltering off the decahydrate crystals, with an approximate compositionof 7.0% Na CO 3.0% Na SO 16% NaCl, and 3% KCl, may be worked up for themanufacture of potassium chloride by evaporating to about one-sixth itsweight at C. or over, in which case sodium chloride, sodium carbonatemonohydrate, and the double salt N a CO 2Na SO would crystallize out andbe removed from the concentrated. potash liquor by filtration orsettling before cooling the liquor to crystallize out potassiumchloride. From 10,000 pounds of such mother liquor a mixture of nearlydry salts would be obtained containing about 1464 pounds of sodiumchloride, 565 pounds of sodium carbonate monohydrate, 379 pounds of thedouble salt Na GO 2Na SO and about 267 pounds of mechanical moisture. Ifto such a mixture we add 1560 pounds of water and agitate for two hoursat a temperature of C., we should obtain 2875 pounds of our standardbrine containin 16% Na CO 14% NaCl, and about 2.8% a 50,, as with thelimited amount of water added there will be an excess of sodium chlorideand double salt l\Ta CO .2Na SO and some sodium carbonate monohydrateleft in the solid phase in contact with the brine. From such'2875 poundsof standard brine may be obtained about 250 pounds of soda ash of highpurity by applying our process already described.

Or we may have a mixture of the dry salts sodium carbonate and sodiumsulphate,

or the hydrates of these salts, together with.

ture at 30 C. or higher temperature until saturation or equilibrium isattained, septhe brine and applying the refrigert p o Having thusdescribedour invention, what we claim is 1. A prooess for themanufacture of soda ash from complex or natural brines containin sodiumcarbonate, sodium sulphate and 0t er salts,which'c0nsists in firstmodifying such brines-to reduce their sodium sulphate content toiessthan four percent by stirring them with an excws of the solid phases ofso-' dium chloride, and sodium carbonate monohydrate or sodium carbonatedecahydrate at a temperature above 20 C. until equilibrium issubta'ntiall attained, allowing the excess ofsaltstose e, and thenchilling such brinesto a temperature above zero degrees centigrade so'18 to cause a substantial part of the sodium carbonate to crystallizeout as sodium carbonate decahydrate, removing and washing the motherliquor from the decahydrate, and driving off the water from suchdecahydrate crystals to form soda ash.

2. A process for the manufacture of soda ash from complex or naturalbrines containing sodium carbonate, sodium sulphate, and

other salts, which consists in stirring such brines-with an excess ofthe solid phases of sodium chloride and sodium carbonate monohydrate orsodium carbonate decahydrate at an approximate temperature of 30 C.until solubility equilibrium is substantially attained, allowing theexcess of salts to settle out at the maintained temperature ofapproximately 30 C., drawing all the settled salts and then chillingsuch brines to a temperature above zero degrees centigrade so as tocause a substantial part of the sodium carbonate to crystallize out assodium carbonate decahydrate admixed with sodium sulphate decahydrate,removing and washing the mother liquor from the decahydrates, anddriving off the water from such decahydrate crystals in a drier orevaporator to form soda ash containing over one per cent sodiumsulphate.

3. A combination of steps in a process for the manufacture of sodiumcarbonate monohydrate from complex or natural brines con taining sodiumcarbonate and other salts, which consists in chilling such brines to atemperature above zero degrees cent'igrade so as to causea substantialpart of the sodium carbonate to crystallize out as sodium carbonatedecahydrate, removing and washing the mother liquor from the decahydratecrystals and melting them up, evaporating ofi a Cportion-of the waterfrom the melted decahyrate crystals so as to cause, the precipitation ofsodium carbonate monohydrate, and separating the sodium carbonatemonohydrate crystals from the mother liquor.

4. A combination of steps in a process for the manufacture of soda ashfrom complex or natural' brines containing sodium carbonate and othersalts, which consists in chilling such brines to a temperature abovezero degrees Centigrade so as to cause a substantial part of the sodiumcarbonate to crystallize out as sodium carbonate decahydrate, removingand washing the mother liquor from the decahydrate crystals and meltingthem up, evaporatin off a portion of the water from the meltedecahydrate crystals so as to cause the precipitation of sodiumcarbonate monohydrate, separating the monohydrate crystals from themother 11 nor, and driving ofi the water frogn the so ium carbonatemonohydrate to form anhydrous sodium carbonate or soda ash.

5. A combination of steps in a process for the manufacture of sodiumcarbonate monohydrate of high purity from complex or natural brinescontaining sodium carbonate, sodium chloride, and an amount of sodiumsulphate over four per cent, which consists in chilling such brines toiatemperature above zero degrees centigrade' so'as to cause a substantialpart of the sodium carbonate to crystallize out as sodium carbonatedecahydrate admixed with a small amount of sodium sulphate decahydratecrystals, and further purifying the sodium carbonate from the ad-'mixture of sodium sulphate and mother liquor impurities by melting upthe decahydrate crystals, evaporating off a portion of the water fromthe solution so as to cause the crystallizing out of sodium carbonatemonohydrate, separating the monohydrate crystals from the mother liquorand washing same.

6. A combination of steps in a process for the manufacture of soda ashof high purity from complex or natural brines containing sodiumcarbonate, sodium chloride, and an amount of sodium sulphate over fourper cent, which consists in" chilling such brines to a temperature abovezero degrees centigrade so as to cause a substantial part of the sodiumcarbonate to crystallize out as sodium carbonate decahydrate admixedwith a small amount of sodium sulphate decahydrate, removing and washingthe mother liquor from such, decahydrate crystals, and further purifyingthe sodium carbonate from the admixed sodium sulphate and mother liquorimpurities by melting up the. decahydrate crystals, evaporating off aportion of the water from the solution so as to cause the crystallizingout of sodium carbonate monohydrate, separating the monohydrate crystalsfrom the mother liquor and washing same, and driving off the water fromthe sodium carbonate monohydrate to form soda ash of high purity.

7. A combination of steps in a process for the manufacture of soda ashof high purity from complex or natural brines containing sodiumcarbonate, sodium chloride, and an amount of sodium sulphate less thanfour per cent, which consists in first modifying such brine to reduceits sodium sulphate content by stirring it with an excess of the solidphases of sodium chloride and sodium carbonate monohydrate or sodiumcarbonate decahydrate at a temperature above 20 C. until equilibrium issubstantially attained, allowing the excess of salts to settle, drawingoff said clear brine, and then chilling the brines to such a temperatureas to cause a substantial part of the sodium carbonate to crystallizeout as sodium carbonate decahydrate without admixture of the crystals ofsodium chloride or sodium sulphate decahydrate, separating thedecahydrate crystals from the brine and thoroughly washing samepractically free from mother liquor, and driving off the Water from thedecahydrate crystals to form soda ash of high purity.

8. A combination of steps in a process for the manufacture of soda ashof high purity from complex or natural brines containing sodiumcarbonate, silica, organic matter, and other salts, which consists infirst modifying such brine to reduce its sodium sulphate content bystirring it with an excess of the solid phases of sodium chloride andsodium caronate monohydrate or sodium carbonate decahydrate at atemperature above 20 (J.

until equilibrium is substantiall attained, allowing the excess of saltsto sett e, drawing off said clear brine, and then making such brinessufficiently alkaline with a caustic alkali to prevent subsequentprecipitation of silica and organic matter, chilling the treated brineto a temperature above zero degrees centigrade so as to cause asubstantial part of the sodium carbonate to crystallize out as sodiumcarbonate decahydrate, separatin the decahydrate crystals from the brinean thoroughly washing same practically free from mother liquor, anddriving ofi the water from the decahydrate crystals to form soda ash ofhigh purity free from silica and organic matter.

9. A combination ofsteps in a process for the manufacture of sodiumcarbonate monohydrate of high purity from complex or natural brinescontaining sodium carbonate, sodium chloride, and an amount of sodiumsulphate less than four per cent, which consists in chilling the brineto such a temperature as to cause a substantial part of the sodiumcarbonate to crystallize out as sodium carbonate decahydrate withoutadmixture of the crystals of sodium chloride or sodium sulphatedecahydrate, removing and washing the mother liquor from suchdecahydrate crystals, and further purifying the sodium carbonate fromthe mother liquor impurities by melting up the decahydrate crystals,evaporating oil a portion of the water from the solution so as to causethe crystallizing out of sodium carbonate monohydrate, separating themonohydrate crystals from the mother liquor and washing same, and dryingthe monhydrate at a low temperature to remove the mechanical waterwithout driving off the water of crystallization.

10. A combination of steps in a process for the manufacture of soda ofhigh purity from complex or natural brines containing sodium carbonate.sodium chloride, and an amount of sodium sulphate less than four percent, which consists in chilling the brine to such a temperature as tocause a substantial part of the sodium carbonate to crystallize out assodium carbonate decahydrate without admixture of the crystals of sodiumchloride and sodium sulphate decahydrate, removing and washing 1 'iemother liquor from such decahydrate crystals, and further purifying thesodium carbonate from the mother liquor impurities by melting up thedecahydrate crystals, evaporating off a portion of the water from thesolution so as to cause the crystallizing out of sodium carbonatemonohydrate, separating the monohydrate crystals from the mother liquorand Washing same. and driving off the water from the sodium carbonatemonohydrate to form soda ash of high purity.

11. A combination of steps in a process for the manufacture of soda ashof high purity from complex or natural brines containing sodiumcarbonate, silica, organic matter, and other salts, which consists infirst making such brines sufiiciently alkaline with a caustic alkali toprevent the subsequent precipitation of silica and organic matter,chilling the treated brine to a temperature above zero degreescentrigrade so as to cause a substantial part of the sodium carbonate tocrystallize out as sodium carbonate decahydrate, removing and washingthe mother liquor from the decahydrate crystals, and further purifc'yingthe sodium carbonate by melting up the emhydrate crystals, evaporatingoil a portion of the water from the solution so as to cause aprecipitation of sodium carbonate monohydrate, separating themonohydrate crystals from the mother liquor and washing same, anddriving off the water from the sodium carbonate monohydrate to form sodaash of hi h purity free from silica and organic co oring matter.

12. A combination of steps in a process for the manufacture of soda ashof high purity from complex or natural brines containing sodiumcarbonate, sodium chloride, and an amount of sodium sulphate in excessof four per cent, which consists in first modifying such brine to reduceits sodium sulphate content to less than fourper cent by stirring itwith an excess of the solid phases of sodium chloride, and sodiumcarbonate monohydrate 61' sodium carbonate decah drate at a temperatureabove 20 C. until equilibrium is substantially attained, allowin theexcess of salts to settle, and then chi mg the, clear decanted brine tosuch a temperature as to cause a substantial part of the sodiumcarbonate to crystallize out as sodium carbonate decahydrate withoutadmixture of the crystale of sodium chloride or sodium sulphatedecahydrate, removing and washing the mother li nor from suchdecahydrate crystals, and rther purif ing the sodium carbonate frommother iquor impurities by melting u the decahydrate crystals,evapcrating o a portion of the water from the solution so as to causethe crystallizing out of sodium carbonate monohydrate separating themonohydrate crystals rom the mother liquor and washing same, anddriving'ofi' the water from the sodium carbonate monoh drate to formsoda ash of high purity.

13. combination of steps in a process for the manufacture of soda ash ofhigh purity from complex or natural brines containing more than thirteenper cent of sodium carbonate, more than four per cent OfSOdlllIIlsulphate, and also sodium chloride, which consists first in heatin theclear brine to such a temperature as wil cause the brine to becomesupersaturated with respect to the doulie salt Na,o0,.2Na,so,,maintaining the brine at this temperature a sufficient length of time toallow part of the sodium carbonate to combine with part of the sodiumsulphate and crystallize out as the double salt Na CO .2Na SO,, therebyreducing the amount of sodium sulphate in solution in the brine, allowinthe double salt to settle out, and then chilhng the clear decanted brineto such a temperature as to cause a substantial part ofthe sodiumcarbonate to crystallize out as sodium carbonate decahydrate withoutadmixture of the crystals of sodium chloride or sodium sulphatedecahydrate, removing and washing the mother liquor from suchdecahydrate crystals, and further urifying the sodium carbonate from themot er liquor impurities by melting 3p the decahydrate crystals,evaporating o a portion of the water from the solution so as to causethe crystallizing out of sodium carbonate monohydrate, separatin themonohydrate crystals from the mother hquor and washing same, and drivingoil the water from the sodium carbonate monohydrate to form soda ash ofhigh purity.

14. A combination of steps in a process for the manufacture of soda ashof high purity from complex or natural brines containing more thanthirteen per cent of sodium carbonate and more than four per cent ofsodium sulphate, which consists first in heatin the clear brine to sucha temperature as wil cause the brine to become supersaturated withrespect to the double salt N a,CO..2Na,SO,, maintaining the brine atthis tein rature for a suflicient len h of time to al ow part of thesodium car onate to combine with part of the sodium sulllphate andcrystallize out as the double salt a CO,.2 Na SO,, agitatin the mixtureat the raised temperature witE an excess of solid sodium chloride torender the precipitation of the double salt NMCO 2Na SO, more complete,thereby materially reducing the amount of sodium sulphate in solution,then settling out the excess of salts and chilling the clear decantedbrine/to such a temperature as to cause a substantial part of the sodiumcarbonate to crystallize out as sodium carbonate decah drate withoutadmixture of the crystals 0 sodium chloride or sodium sulphatedecahydrate, removing and washing the mother li nor from suchdecahydrate c stals, and rther urifying the sodium car nate from the moter liquor impuritiesiby melting up the decahydrate crystals, evaporatingoil a portion ofthe water from the solution so as tocause the cstallizing out of sodium carbonate mono ydrate, separating themonoliydiate crystals from the mother liquor an washing same, anddriving ofl the water from the sodium carbonate monohydrate to form sodaash of high purity;

15. A combination of steps in a rocess for the manufacture of soda ashof high purity fromthe brines of Owens Lake containing the chlorides,carbonates, sulphates and borates of sodium and potassium, as well asdissolved v and 2.8%

,silica and organic coloring matter, which consists in first preparing abrine of the standard and invariant composition of approximately 16%sodium carbonate, 14.5% of the chlorides of sodium and potassium, sodiumsulphate, by stirring such brines as naturally exist on or under thesurface of Owens Lake with an excess of the solid phases of sodiumchloride, and sodium carbonate monohydrate or sodium carbonatedecahydrate at an approximate temperature of 30 C., until solubilityequilibrium is sub: stantially attained, allowing the excess of salts tosettle out at the maintained temperature of approximately 30 (1.,drawing olf the settled brine, then adding to the clear decanted brine asmall amount of caustic alkali to maintain it sufiiciently alkaline toprevent the subsequent precipitation of silica and organic coloringmatter, chilling the treated brine to such a temperature as to cause asubstantial part of the sodium carbonate to crystallize out as sodiumcarbonate decahydrate without admixture of the crystals of sodiumchloride or sodium sulphate decahydrate, removing and washing the motherliquor from such decahydrate crystals, and further purifying the sodiumcarbonate from the mother liquor impurities by melting up thedecahydrate crystals, evaporating 011' a portion of the water from thesolution so as to cause the crystallizing out of sodium carbonatemonohydrate, separating the monohydrate crystals fifrom the motherliquor and washing same, and

driving off the water from the sodium carbonate monohydrate to form sodaash of high purity and practically free from silica and organic coloringmatter.

16. The process of separating and recovering sodium carbonatedecahydrate in a purified state from the brines of Owens Lake,containing the chlorides, carbonates, sulphates, and borates of sodiumand potassium, Which consists in filling a large storage pond orreservoir with the clear surface brine from the crystal body of the lakein the hot summer months when the temperature of the surface brineexceeds 20 C., such brine having had its sodium sulphate contentnaturally reduced by the crystallizing out of the double salt Na CO 2NaSO due to the action of heat to such a point that when the brine ischilled so as to cause a substantial part of its sodium carbonatecontent to crystallize out there will be no crystallizing out of sodiumsulphate decahydrate, such brine being also saturated with respect tosodium carbonate and sodium chloride at the temperature prevailing, thenallowing the brine in the storage pond or reservoir to cool by naturalmeans in the winter months, thereby crystallizing out only sodiumcarbonate decahydrate, drawing or draining off from the storage pond themother liquor from the crystals, harvesting the decahydrate crystals andseparating the adhering or entrained mother liquor from same, andwashing the decahydrate crystals free from mother liquor.

17. The process of separating and recovering sodium carbonate in apurified state from the brines of Owens Lake containing the chlorides,carbonates, sulphates, and borates of sodium and potassium, whichconsists in filling a large storage pond or reservoir with the ,clearsurface brine from the crystal body of the lake in the hot summer monthswhen the temperature of the surface brine exceeds 20 C., such brinehaving had its sodium sulphate content naturally reduced by thecrystallizing out of the double salt Na Co 2Na SO due to the action ofheat to such a point that when the brine is chilled so as to cause asubstantial part of its sodium carbonate content to crystallize outthere will be no crystallizing out of sodium sulphate decahydrate, suchbrine being also saturated with respect to sodium carbonate and sodiumchloride at the temperature prevailing, then allowing the brine in thestorage pond or reservoir to cool by natural means in the winter months,thereby crystallizing out only sodium carbonate decahydrate, drawing ordraining otf from the storage pond the mother liquor from the crystals,melting up the crude decahydrate crystals with water or steam, andseparating the sodium carbonate from the mother liquor impurities byrecrystallization, carbonation, or other method.

18. A combination of steps in a process for the manufacture of soda ashof high purity from natural deposits of dry salts containing sodiumsulphate, an amount of sodium carbonate greater than the molecularproportion of one molecule of sodium carbonate to two molecules of thesodium sulphate present, and an excess of sodium chloride, and othersalts, which consists in agitating such mixture of salts with a limitedamount of water at a temperature above 20 C. until the resulting brinehas become saturated with respect to sodium carbonate monohydrate,sodium chloride, and the double salt N a CO 2N a SO settling out theexcess of salts, drawing ofi' the settled brine, and then chilling theclear decanted brine to such a temperature as to cause a substantialpart of the sodium carbonate to crystallize out as sodium carbonatedecahydrate without admixture of the crystals of sodium chloride orsodium sulphate decahydrate, removing and washing the mother liquor fromsuch decahydrate crystals, and further purifying the sodium carbonatefrom the mother liquor impurities by melting up the decahydratecrystals, evaporating oil a portion of the water from the solution so asto cause the crystallizing out of sodium carbonate monohydrate,separating the monohydrate crystals from the mother liquor and washingsam and driving off the water from the sodium carbonate monohydrate toform soda ash of high purity.

19. A com ination of steps in a process for the manufac ure of soda ashof high purity from a mixture of tail salts such as are a waste productin the manufacture of potassium chloride by the evaporation of brinescontaining potassium and sodium chlorides, sodium carbonate, and sodiumsulphate, su'ch' tail salts consisting essentially of sodium carbonatemonohydrate, the double salt Na CO .2Na,SO and an excess of sodiumchloride, which consists in adding a limited amount of water to suchmixture of salts not quite suflicient to dissolve all the sodiumcarbonate monohydrate, agitating the mixture at a temperature above 20C. until the resulting brine has become saturated with respect to sodiumcarbonate monohydrate, sodium chloride, and the double salt Na CO 2Na SOsettling out of the excess of salts, drawing oil .the settled brine, andthen chilling the clear decanted brine to such a temperature as to causea substantial part of the sodium carbonate to crystallize out as sodiumcarbonate decahydrate without admixture of the crystals of sodiumchloride and sodium sulphate decahydrate, removing and washing themother liquor from such decahydrate crystals, evaporating off a portionof the water from the solution so as to cause the crystallizing out ofsodium carbonate monohydrate, separating the monohydrate crystals fromthe mother liquor and washing same, and driving ofi' the water from thesodium carbonate monohydrate to form soda ash of high purity. a

20. A combination of steps in a rocess for the manufacture of soda ashof high purity from a mixture of tail salts such as are a waste roductin the manufacture of otassium c loride by the evaporation of rinescontaining potassium and sodium chlorides, sodium carbonate, and" sodiumsulphate, such salts consisting essentially of sodium carbonatemonohydrate the double salt Na,CO,.2Na,SO and a deficiency of sodiumchloride, which consists in adding a limited amount of water to such amixture of salts not quite suflicient to dissolve all the sodiumcarbonate monolliiydrate, then adding an excess of sodium 0 oride in thesolid state, agidecahydrate crystals, and further purifying the sodiumcarbonate from the mot er liquor impurities by melting up the decahdrate crystals, evaporating off a portion of t e water from the solutionso as to cause the crystallizing out of sodium carbonate monohydrate,separating the monohydrate crystals from the mother liquor and washingsame, and driving off the water from the sodium carbonate monohydrate toform soda ash of high purity.

In witness whereof, we have hereunto set our hands this 21st da ofDecember, 1929.

ALEX S C. HOUGHTON. JAMES G. MILLER.

tatin the mixtureat a temperature above 20 until the resulting brlne hasbecome saturated with respect to sodium carbonate monohydrate, sodiumchloride, and the double salt Na,CO .2Na,SO,, settling out the excess ofsalts drawin oil the settled brine, and then chilling the c ear decantedbrine to such a temperature as to cause a substantial part of the sodiumcarbonate to crystallize out as sodium carbonate decahydrate withoutadmixture of the crystals of sodium chloride or sulphate decahydrate,removmg and washing the mother liquor from such

